Interesting template. Not sure it's something I'd personally want to use, but if you like it, cool.
Regarding the flexibility of templates, I have two comments.
First, to paraphrase a pirate, I see templates as "more what you'd call "guidelines" than actual rules."
Secondly, there are two templates, one explicitly in the book, and one indirectly referenced, that can be used to justify almost any combination of powers - Emissary of Power and Scion. I will offer an example of each:
A friend of mine is playing a monster-hunting swordsman named Roland who wields Durendal, the legendary sword (this was written before Durendal was ever mentioned in the actual Dresden books). He is modeled as an Emissary of Power, with Marked by Power, Supernatural Toughness, Inhuman Strength, and Inhuman Recovery (the last three all discounted by the Item of Power rebate, as they come from the sword). The sword, Durendal, is sentient and chose Roland as a worthy bearer.
Recently, I was told by my GM that I should write up a new character to play, as my last one has been mind-raped a few too many times (long story). I was flipping through the books and decided that both Modular Abilities and Glamours looked like fun powers. A changeling would be the obvious choice if I wanted Glamours, but Modular Abilities is harder to justify, especially as I wanted to take it without True Shapeshifting or Beast Change. Eventually, I settled on being a Scion of a Rakshasa, a sort of Hindu demon known for illusion and shapeshifting powers.
I feel that, when playing in the standard Dresden setting, the default list of templates covers 95% of what you might want to play. For the remaining 5%, I don't think a template is actually needed, so long as GM and player can agree on reasonable aspect, stunt, and power musts, options, and limits.
The only template that I wish they would have put in is "Wielder of an Item of Power" - a catch-all template for characters whose only source of supernatural abilities is an item of power.